1. Field of the Invention (Technical Field)
The invention relates to surgical correction of human eye refractive errors such as presbyopia, hyperopia, myopia, and stigmatism. More particularly, it is related to surgical corrections of such errors with implantation of a prosthesis for increasing or decreasing the eye length and scleral curvatures, and thus bringing the retina/macula region to coincide with the focal point of the eye.
2. Background Art
There are many refractive errors associated with the human eye. When the focal point of images is formed in front of the retina/macula region due to too much refraction of light rays, the refractive error is called myopia or near-sightedness. When, on the other hand, the focal point of images lie outside the eye behind the retina/macula region due to too little refraction of light rays, the refractive error is called either hyperopia or far-sightedness or presbyopia. These problems can be surgically corrected by either changing the eye length or scleral curvatures. In case of presbyopia, as individuals age, the human eye loses its ability to focus on nearby objects. This condition, known as presbyopia, is due to a progressive loss in the elasticity of the lens of the eye, such that the ciliary muscles which normally force the lens, through the action of zonule fibers on the lens capsule, in a rounded shape to accommodate near objects can no longer exert the necessary changes in the lens"" shape.
The conventional optometric solution to the problems of myopia, hyperopia, and presbyopia is a prescription of glasses or reading glasses or, for individuals who already require glasses to correct other refractive errors such as myopia or astigmatism, a prescription of bifocal or multifocal glasses.
This century has witnessed a revolution in the surgical treatment of ophthalmic disorders and refractive errors of the human eye. This revolution ranges from corneal implantations, cataract extraction, phacoemulsification of the lens, intraocular lens implantation, glaucoma implants to control the intraocular pressure, radial keratotomy, excimer laser ablation of the cornea, trabeculoplasty, iridotomy, virectomy, and the surgical buckle treatment of retinal detachment. The recent surgical solutions to myopia, hyperopia, and stigmatism have been laser photorefractive keratectomy (PRK), Lasik (laser-assisted in-situ keratomileusis) and RK or radial keratotomy. Modern techniques proposed to correct human eye refractive errors have been corneal implants (Intacs, Keravision rings, Silvestrini, intrastromal corneal ring (ICR) ) and scleral implants (SASI, Presbycorp implants, Schachar Accommodative Scleral Implants).
The effective focal length of the human eye must be adjusted to keep the image of the object focused as sharply as possible on the retina. This change in effective focal length is known as accommodation and is accomplished in the eye by varying the shape of the crystalline lens. This is necessary for the human eye to have clear vision of objects at different distances. Generally speaking, in the unaccommodated normal vision, the curvature of the lens is such that distant objects are sharply imaged on the retina. In the unaccommodated eye, close objects are not sharply focused on the retina and their images lie behind the retinal surface. In order to visualize a near object clearly, the curvature of the crystalline lens is increased, thereby increasing its refractive power and causing the image of the near object to fall on the retina. The change in shape of the crystalline lens is accomplished by the action of ciliary muscle by which the radial tension in the lens is reduced, according to classical Helmholtz theory of accommodation, and it becomes more convex. Based on Helmholtz theory, in the unaccommodated human eye the lens and its capsule are suspended on the optical axis behind the pupil by a circular assembly of many radially directed collagenous fibers, the zonules, which are attached at their inner ends to the lens capsule and at their outer ends to the ciliary body, a muscular constricting ring of tissue located just within the outer supporting structure of the eye, the sclera. The ciliary muscle is relaxed in the unaccommodated eye and therefore assumes its largest diameter. According to the Helmholtz classical theory of accommodation, the relatively large diameter of the ciliary body in this unaccommodated condition, causes a tension on the zonules which in turn pull radially outward on the lens capsule, making it less convex. In this state, the refractive power of the lens is relatively low and the eye is focused for clear vision of distant objects. When the eye is intended to be focused on a near object, the muscles of the ciliary body contract. This contraction causes the ciliary body to move forward and inward, thereby relaxing the outward pull of the zonules on the equator of the lens capsule and reducing the zonular tension on the lens. This allows the elastic capsule of the lens to contract causing an increase in the sphericity of the lens, resulting in an increase in the optical refraction power of the lens. Recently, Schachar (whose inventions are discussed below) has proposed a radically different theory of accommodation which refutes the Helmholtz theory.
Accordingly, the present invention relates to systems and methods of compensating presbyopia, hyperopia, myopia, and stigmatism by actively changing the length of the eye globe in the direction of optical axis or its curvature, on demand, using active constricting (sphinctering) artificial muscles as active scleral bands. The scleral band in the form of an active and smart constricting/expanding band comprising an active prosthesis which can be remotely powered by small inductive generators that can be placed near the eye, preferably behind the ears or under the skin on the shoulder or on an arm band.
There are several prior art devices and methods in the form of implants and prostheses for the surgical correction of presbyopia, hyperopia, and myopia.
U.S. Pat. No. 5,354,331 to Schachar, discloses how presbyopia and hyperopia are treated by a method that increases the amplitude of accommodation by increasing the effective working distance of the ciliary muscle in the presbyopic eye. This is accomplished by expanding the sclera in the region of the ciliary body. A relatively rigid band having a diameter slightly greater than that of the sclera in that region is sutured to the sclera in the region of the ciliary body. The scleral expansion band comprises anterior and posterior rims and a web extending between the rims, the anterior rim having a smaller diameter than the posterior rim.
In U.S. Pat. No. 5,465,737 to Schachar, the teachings are similar to those of the ""331 patent, except that by weakening the sclera overlying the ciliary body, by surgical procedures or treatment with enzymes, heat or radiation, whereby intraocular pressure expands the weakened sclera, or by surgical alloplasty. The effective working distance of the ciliary muscle can also be increased by shortening the zonules by application of heat or radiation, by repositioning one or both insertions of the ciliary muscle or by shortening the ciliary muscle. Presbyopia is also arrested according to the invention by inhibiting the continued growth of the crystalline lens by application of heat, radiation or antimitotic drugs to the epithelium of the lens. Primary open angle glaucoma and/or ocular hypertension can be prevented and/or treated by increasing the effective working range of the ciliary muscle according to the invention.
U.S. Pat. Nos. 5,489,299; 5,722,952; 5,503,165; and 5,529,076 to Schachar contain essentially the same ideas as U.S. Pat. Nos. 5,354,331 and 5,465,737 with some improvements such that presbyopia and hyperopia are treated by a method that increases the amplitude of accommodation by increasing the effective working distance of the ciliary muscle in the presbyopic eye. The effective working distance of the ciliary muscle is increased by shortening the zonules by application of heat or radiation, by repositioning one or both insertions of the ciliary muscle or by shortening the ciliary muscle. Presbyopia is also arrested by inhibiting the continued growth of the crystalline lens by application of heat, radiation or antimitotic drugs to the epithelium of the lens. Primary open angle glaucoma and/or ocular hypertension can be prevented and/or treated by increasing the effective working range of the ciliary muscle.
U.S. Pat. No. 6,007,578 to Schachar, discloses how presbyopia is treated by implanting within a plurality of elongated pockets formed in the tissue of the sclera of the eye, transverse to a meridian of the eye, a prosthesis having an elongated base member having an inward surface adapted to be placed against the inward wall of the pocket and having a ridge on the inward surface of the base extending along at least a major portion of the major dimension of the base. The combined effect of the implanted prostheses is to exert a radially outward traction on the sclera in the region overlying the ciliary body which expands the sclera in the affected region together with the underlying ciliary body. This restores the effective working distance of the ciliary muscle in the presbyopic eye and thereby increases the amplitude of accommodation. Hyperopia, primary open angle glaucoma and/or ocular hypertension can be treated by increasing the effective working distance of the ciliary muscle.
U.S. Pat. No. 6,006,756 to Shadduck, discloses a system and technique called magnetoresonant induction of an intrastromal implant that is adapted for corneal re-shaping. The technique is utilized to correct mild to high hyperopia and presbyopia by steepening the anterior corneal curvature in a single treatment, or in periodic treatments over the lifetime of the patient. The system comprises a combination of components including (i) at least one implantable magnetoresonant intrastromal segment, and (ii) an oscillating magnetic field generator together with a dosimetry control system including at least one emitter body adapted for positioning proximate to the patient""s eye and intrastromal implant. The system can deliver thermal effects to appropriate stromal lamellae by non-contact inductive heating of the implant which in turn contracts or compresses stromal collagen fibrils into a circumferential cinch about an anterior layer of the cornea and steepens the anterior corneal curvature. A dosimetry control system controls the power level and duration of exposure of the oscillating magnetic field(s) and may be combined with intraoperative corneal topography.
U.S. Pat. No. 5,147,284 to Fedorov, et al, teaches a device for restoration of visual functions in cases of affected optic nerve and retina with an electromagnetic field radiator emitting the latter field into the region of the eyeball and an electromagnetic field receiver adapted to interact with the radiator. Both of these exert an electrostimulation effect on the optic nerve and the retina. The electromagnetic field radiator is a source of a pulsed magnetic field and is shaped as an electromagnet provided with an adjuster of a distance between the end of the electromagnet and the electromagnetic field receiver, which is in effect an inductor having lead wires furnished with electrodes whose active surface exceeds 10 mm2. A method for restoration of visual functions in cases of affected optic nerve and retina consists in conducting electrostimulation of the eyeball, for which purpose an inductor is implanted into the orbit on the sclera of the posterior portion of the eyeball in such a manner that one of the inductor electrodes is positioned nearby the external tunic of the optic nerve, while the other electrode is fixed on the sclera in the area of the eyeball equator, whereupon a pulsed magnetic flux is applied remotely to the eyeball portion carrying the inductor, the magnetic field induction being from 0.1 T to 0.25 T, while the pulsed magnetic field is simultaneously brought in synchronism with pulsation of the internal carotid artery.
U.S. Pat. No. 5,782,894 to Israel, discloses a device and method for treating presbyopia by which the ciliary muscles of the eyes are electrically stimulated when the internal rectus muscles of the eyes are activated in order to focus the eyes on objects within the near field of vision. The amounts of electrical stimulation can be adjusted according to the individual needs of a patient and are preferably in direct proportion to the amounts of contraction of the internal muscles.
U.S. Pat. No. 4,961,744 to Kilmer, et al, discloses a surgical apparatus for inserting a plastic, split end, adjusting ring into the stroma of the cornea of the eye wherein the adjusting ring includes, as a part thereof, a dissecting head to part the stroma and provide a pathway for the adjusting ring as the ring is rotated. The ends of the adjusting ring are moved to change the shape of the cornea to a desired shape in accordance with the desired visual correction after which the ends of the adjusting ring are fixably joined to maintain the desired shape.
U.S. Pat. No. 5,300,118 to Silvestrini, et al, discloses an intrastromal corneal ring (ICR) that is adjustable in thickness and has an elongated, flexible, preferably transparent or translucent body which forms a circle. The ICR is of a size such that it can be inserted into a human eye and is comprised of a material which is compatible with human ocular tissue. The thickness of the ring can be adjusted so that it is not necessary to stock a plurality of different rings of different sizes to be used in connection with a method of adjusting the shape of the cornea of the eye. A plurality of different embodiments of ICRs are disclosed each of which are adjustable in terms of their thickness. The thickness may be adjusted prior to the insertion of the ICR into the cornea and may not be further adjustable after insertion. However, in accordance with preferred embodiments, the ICR is inserted at a thickness which is believed to be proper and may thereafter be further adjusted in order to precisely define the desired thickness and thereby more precisely adjust the shape of the cornea, and focus the light entering the eye on the retina.
U.S. Pat. No. 5,824,086 to Silvestrini, discloses a pre-formed intrastromal corneal insert. It is made of a physiologically compatible polymer and may be used to adjust corneal curvature and thereby correct vision abnormalities. The insert or segment may also be used to deliver therapeutic or diagnostic agents to the interior of the cornea or of the eye. The insert subtends only a portion of a ring or xe2x80x9carcxe2x80x9d encircling the anterior cornea outside of the cornea""s field of view. The invention also includes a procedure for inserting the device into the cornea.
U.S. Pat. No. 6,051,023 to Kilmer, et al, discloses a surgical apparatus for inserting a plastic, split end, adjusting ring into the stroma of the cornea of the eye wherein the adjusting ring includes, as a part thereof, a dissecting head to part the stroma and provide a pathway for the adjusting ring as the ring is rotated. The ends of the adjusting ring are moved to change the shape of the cornea to a desired shape in accordance with the desired visual correction after which the ends of the adjusting ring are fixably joined to maintain the desired shape.
U.S. Pat. No. 5,888,243 to Silverstrini, discloses an intrastromal corneal ring housing comprising at least one outer layer of a physiologically compatible polymer having a low modulus of elasticity, which polymer may be hydratable and may be hydrophilic. The inner portion of the hybrid intrastromal corneal ring may be hollow or may contain one or more physiologically compatible polymers.
U.S. Pat. No. 5,766,171 to Silvestrini, teaches a device and procedure for the correction of optical abnormalities in a human eye. It involves use of an inventive electrosurgical energy probe with specific physical configurations. The process preferably utilizes a high frequency RF electro-desiccation or ablation device. The procedure involves the initial step of forming at least one access site allowing access to the corneal volume behind the Bowman""s Layer. It is placed in the anterior surface of the cornea through and ending posterior to the Bowman""s layer of the eye. The electrosurgical probe is then introduced into the access site, and depending upon the visual abnormality to be corrected, the probe is activated to adjust the volume of the corneal stromal layers through ablation or desiccation. The shape of the volume desiccated or ablated is dependent upon the aberration to be corrected. In other instances, such as for the treatment of astigmatism, certain smaller sections of the corneal volume may be shrunk. In certain circumstances, the Bowman""s layer may be cut to allow the curvature of the cornea to change after the corneal volume adjustment. These relief cuts may be radial, circular, semicircular or any other form appropriate for the option adjustment needed.
The invention disclosed is an apparatus and method to create on-demand correction of refractory errors in the eye by the use of an active and smart scleral band equipped with composite artificial muscles. The scleral band induces scleral constriction or expansion, similar to a scleral buckle in retinal detachment surgical correction. The scleral band is an encircling composite silicon band around the middle of the eye""s globe to provide relief of intraretinal tractional forces by indentation of the sclera as well as repositioning of the retina and choroid. It can also induce myopia, depending on how much tension is placed on the buckle, by increasing the length of the eye globe in the direction of optical axis. By using the scleral band, one can actively change the axial length of the scleral globe in order to induce refractive error correction. For example, inducing a slight degree of myopia, one to three diopters has been shown to enable presbyopes to read without the use of glasses.
The present invention creates an active smart band to encircle the sclera, which constricts or expands in such a way to induce temporary myopia or hyperopia. The smart band is implanted under the conjunctiva, preferably under the extraocular muscles. This band is secured to the sclera in a similar manner used in scleral buckle surgery. The smart band is either a singular or composite contractile artificial muscle which will be transcutaneously inductively heated to raise its temperature to a critical value (about 40 degrees Celsius) at which the smart muscle band will resiliently contract, preferably up to 6% or more. This will create a mild scleral constriction which will in turn cause the length of the eye to increase, and the retina/macula region to move back to coincide with the focal point of the image of a near object, to accommodate presbyopia, and hyperopia by inducing a temporary mild myopia, thus correcting the presbyopic vision. The scleral band preferably comprises an interior body of contractile Shape-Memory Alloy (SMA) actuator wires or ribbons with attachable ends to make an endless band encased or embedded inside a silicone rubber sheath or cladding. The rubber cladding acts as a resilient structure to store potential energy when the SMA wires or ribbons contract and use the stored resilient (springy) potential energy to stretch the contractile wires or ribbons back to their initial relaxed length when the wires or ribbons cool off and expand. This also helps relax the sclera back to its initial dimensions when the temperature is reverted back to the normal body temperature. The SMA wires or ribbons go through a solid Martensite-Austenite phase transformation during their contraction, i.e., as they are transcutaneously inductively heated, at the critical Austenite start temperature, for example 40 degrees Celsius. The wires contract and create enough constricting force to compress the silicone rubber cladding thus buckling the sclera. This creates an indentation of the sclera which causes the eye to lengthen and thus presbyopia or hyperopia are accommodated. By turning the remote inductive heating generators off, the temperature of the smart band reverts back to normal or Martensite finish temperature. The SMA wires or ribbons make a solid phase transformation to Martensite phase, thus, enabling the silicone rubber cladding resilient unbuckling force to stretch the wires or ribbons back to their normal stress-free state. This will induce Emmetropia (xe2x80x9cnormalxe2x80x9d vision). Another embodiment of the smart scleral band is an armature winding made with gold ribbons to act as an inductive heating coil to heat up the SMA wires. The inductive generators (battery-operated magneto-resonant coils) can be housed behind the ears of the person wearing the scleral prosthesis, worn like an arm band or surgically implanted under the skin in an easily accessible location and preferably can be tuned on or off by the person wearing them by a touch of a finger (on-demand virtual reading glasses).
Other alternative embodiments are scleral constricting bands equipped with other types of composite artificial muscles such as resilient composite shape memory alloy-silicone rubber implants in the form of endless active scleral bands, electroactive ionic polymeric artificial muscle structures, electrochemically contractile endless bands of ionic polymers such as polyacrylonitrile (PAN), thermally contractile liquid crystal elastomer artificial muscle structures, magnetically deployable structures or other deployable structures equipped with smart materials such as piezocerams, piezopolymers, electroactive and electrostrictive polymers, magnetostrictive materials, and electro or magnetorheological materials.
To install the scleral band the following surgical procedure is performed. A 360-degree conjunctiva peritomy is performed. The conjunctiva is carefully dissected free from the sclera. Each of the extraocular muscles are isolated and freed from the check ligaments. The composite artificial muscle constricting band is then placed underneath the extraocular muscles and then secured together creating a 360 degree band encircling the sclera. The band is then secured to the sclera using 6.0 nylon sutures, or the like. In the alternative, the artificial muscle band can be placed 3 mm from the sclera and the band implanted one half thickness into the sclera. The simplest method of implantation is similar to the method used for scleral buckle surgery. The two alternative positions will increase the axial length and local curvature of the globe. The composite artificial muscle will deactivate on command returning the axial length to its original position and vision back to normal (emmetropic vision).
A primary object of the present invention is to create on-demand correction of refractory errors in the eye by the use of an active and smart (computer-controllable) scleral band equipped with composite artificial muscles.
Another object of the present invention to create an active smart band to encircle the sclera, which will constrict or expand in such a way to induce temporary myopia or hyperopia.
A primary advantage of the present invention is that the installation of the present invention on a human eye does not include destructive intervention like the present implantable devices or laser correctional surgery such as RK, PRK or Lasik.
Another advantage of the present invention is that this will be an active and smart mechanism to be implemented when one is reading.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.